This invention relates in general to machines for automatically applying termination paste to electronic components during the process Of terminating the components, e.g. multilayer ceramic capacitors, and in particular to machines which dip planar arrays of such components into a sheet of viscous termination paste deposited on a planar surface.
As used herein the term "electronic component" shall refer to multilayer ceramic capacitors, chip resistors, metal film resistors, multilayered ceramic chip varistors, and any other device to which termination paste can be applied in the manner described herein.
An example of how this invention can be used to advantage is in the art of manufacturing multilayer ceramic capacitors, commonly called chip capacitors. In this art, once a chip is created the ends of the chip must be terminated, i.e., capped with an electrically conductive material to provide internal and external electrical connections. The ends are conventionally terminated in a multi-step process wherein they are each coated with a viscous termination "paste", heated to remove volatile liquid ingredients of the paste, and further heated to remove resins and fuse the remaining ingredients (glass frits and conductive particulate) to the chip ends.
In the prior art, elastomeric carriers have been devised which can each hold an array of spaced ceramic capacitor chips such that unterminated ends of the chips protrude a uniform distance from a common planar face of the carrier, and apparatuses have been devised which receive such carriers and dip the protruding chip ends into a uniform sheet of termination paste spread on a planar surface commonly called a platen.
Heretofore such platens have been either stationary or reciprocally movable within a range. For stationary platens the process of dipping the protruding ends has heretofore involved at least the steps of (1) passing a "doctoring" device over the platen, i.e., a device which paints uniform sheets of termination paste onto the platen, (2) lowering the carrier sufficiently to dip the chips' ends into the paste, (3) raising the carrier, and (4) passing a device over the platen to scrape off leftover paste. While the doctoring and scraping operations may be combined into a single step, there are nevertheless several disadvantages to a stationary platen. For one, the spacing of the carrier above the platen during doctoring and scraping must be great enough to allow the doctoring/scraping devices to pass beneath. This means that the dipping stroke is much longer than if such passage beneath was not necessary, and a longer dipping stroke translates into fewer strokes per unit time for a given dipping head drive. Also, the dipping rate is limited by the delay between dips while the doctoring/scraping devices move back and forth over the platen. Such back and forth movement is not time efficient.
For the movable platens the process of dipping the protruding ends has heretofore involved at least the steps of (1) moving the platen so that it passes beneath a doctoring device to paint a sheet of paste on the platen, (2) moving the platen back beneath the carrier, (3) lowering the carrier sufficiently to dip the chips' ends into the paste, (4) raising the carrier, and (4) again moving the platen so that it passes beneath a device which scrapes off leftover paste. While the doctoring and scraping operations may be combined into a single step, there are nevertheless several disadvantages to such a movable platen. The dipping rate is limited by the delay between dips while the platen is moved back and forth beneath the doctoring/scraping devices. This reciprocating movement is more time consuming than if movement were in one direction only, and the stroke of this back and forth movement increases as the length of the carrier increases. Moreover, precisely timed actuators must be used to raise and lower the scraping device, and open and close a doctor blade while the platen reciprocates beneath.
Another problem exists in the prior art. Components being held by the elastomeric carriers are often pulled loose by the adhesive force of the paste. In these carriers the components are inserted into respective perforations in an elastomeric sheet. The perforations are slightly undersized with respect to the components they are designed to hold, and so the components are held by friction between them and the elastic walls of their respective slots. For various reasons the adhesive force of the paste combined with gravity can sometimes overcome the friction and dislodge components. These loose components can foul up subsequent operations, particularly in apparatuses that scrape the leftover paste back into the reservoir from which the sheets are painted. Most, if not all, prior art apparatuses do this. The presence of dislodged components in the reservoir can cause streaks of discontinuity in subsequent sheets being painted with obvious undesirable results.
This invention overcomes the above-described time related disadvantages of both the stationary and reciprocating platens and the problem of dislodged components. Further advantages and attributes will be seen from a reading of the text hereinafter.